Telegraph hub repeater circuit



United States Patent Ollice search Corporation, Forest Park, Ill., a corporation of Illinois Filed Nov. 10, 1959, Ser. No. 852,106 9 Claims. (Cl. l78-73) The present invention relates to an improved telegraph repeater unit and more particularly to a transistor-ized circuit which is a direct plug-in replacement for existing coupling units in commercial systems of the general type disclosed, for example, in U.S. Patent Nos. 2,607,852 to Rea and 2,636,942 to Davey. In commercial practice certain operating conditions and voltages have been standardized and are well known to those skilled in lthis art, and the following description will assume an understanding of this art.

A principal object of the present invention is to provide an improved inexpensive, easy to service, direct plug-in replacement for prior leg coupling units commonly referred to as a 144A1 circuit. While the present invention has essentially the same electrical characteristics viewed externally, because of being a transistorized circuit adapted to use three transistors of the `same type, considerable variation of internal circuitry has been found necessary to provide a practical unit which will comply with the strict testing and exacting standards 4reqin'red in this industry,

Referring now 4to the drawing wherein the circuit diagram of my improved coupling unit is illustrated, the uni-t comprises a receive leg having the usual receive relay with -alternate contacts connected to positive and negative voltages and connected to the receive hub. The send hub is conventionally connected, either directly or through a regenerative repeater by contacts l2 and 14, to the receive hub. The send leg is connected vfrom the send hub. Varying numbers of from 2 to l0 or more lines are connected to the receive and send hubs, each having a plug-in unit such as that illustrated in the drawing.

With the receive (R) leg of the repeater to which the unit is connected in the mark condition, and the receive and send hubs also in the mark condition, the voltages at the various points inthe circuit Iare as indicated for condition MM. In these designations, the iirst letter'indicates the condition of the R leg of the repeater associated with the unit, and the second letter indicates the condition of the R leg of another repeater connected through a coupling unit to the same receive hub. In the MM lcondition, transistor T1 has +22 volts on its base and +8 volts on its emitter and is therefore normally non-conducting since no current liows from base to emitter when the base is positive with respect to the emitter.

Considering transistor T2, the voltage applied to the base of this transistor results from the +130 volts through R4 and R5. This voltage, as applied to the one terminal of capacitor C1, is limited to +8 volts .by the diode across the collector and emitter of T1. The +8 volts on the ungrounded terminal of capacitor C1 is applied directly to the base of T2 through diode D3 which shunts resistor R9 for this polarity. TZ is therefore normally Inon-cornlucting, and under this condition will have no effect on the operation of T3.

Considering transistor T3, with the sen-d hub in the MM condition, a voltage of +60 is conventionally available ony the send hub and is applied through R6 to the base of T3. rllhis voltage is reduced by the -130 volts applied to the base of T3 through R15. The circuit through R is for the purpose of changing the +60 to 30 (the conventional space signal voltage on the send hub) voltage swing on the `send hub, which has a mid- Patented May s, 1962 point of +15, to a swing of +43 to +39 at the base of T3 which has a mid-point of +2. This centers the swing around approximately +2 volts lon the emitter of T3 and results in no bias to transmission -from the send hub through T3. n

With the send hub at +60 corresponding to a mark signal voltage, and the voltage on the base of T3 at +43, T3 will be non-conducting. Under this condition, the current Ithrough the windings of the send relay will be approximately seven mils, as determined by volts through R18 to the windings. Since the resistance of the windings of the relay is only 272 ohms, the parallel branch of 5.6 K ohms to ground will have little eiect on the winding current. The seven mills current will be in a marking direction to hold the armature of the relay on mark. i

.The voltage at the collector of T3 is limited to -24 volts by diode D4. Current will be flowing through R14 and D4 while T3 is non-conducting. The purpose of diode D4 is to limit the voltage at the collector of transistor T3 to a value within the yrating of the transistor. Resistor R19 is only for the purpose of protecting the transistor at a time when a -24 volt fuse might blow. In this case, with the -24 volts absent, the path to ground through R19 will limit the vol-tage at the collector of transistor T3 -to about -26 volts.

yIn the idle and in the marking condition of this circuit, all three transistors are non-con2ducting- When the receive hub `goes spacing due to a space being received on another repeater connected to the hub, the lsend hub goes spacing, its voltage becomes 30, and the voltage applied to the base of T3 becomes +39. This causes transistor T3 to conduct and a current of approximately 14 milliamps to flow through R14, through transistor T3 and the relay windings in a spacing direction to ground. This 14 rnilliamp lspacing current overrides ,the 7 nulli-amp marking current Ifrom +130 volts through R1=8 and causes a resultant current of 7 milliamp 'spacing which operates the relay to spacing. Thus, any space signal occurring on the send hub due to a space being received from any other repeater on the hub is transmitted to the send relay directly with no holding action taking place, since transistor T2 is non-conducting under this condition. Y Y.

The operation of the receive relay to space of the repeater connected to the R leg of the control circuit (Condition SM) causesl the voltage on the receive hub to change of +60 to 30. At the same time the voltage on the send hub will change to -30 immediately if there is no regenerative repeater between the receive and send hubs, or in about halfvavjunit pulse length later if there is a regenerative repeater between fthe two hubs. The function of `the control circuit in this case'is to prevent .the space voltage on the send hub from operating the send relay to spacing and thus sending a space back to the originator of the space pulse on the receive siderof the circuit. When the receive relay -in the lreceive leg of the illustrated circuit goes to spacing, 'the voltage at `the top of R4 changes from +130 to about 120 volts, which causes a voltage ofabout 22 volts at the junction of R4 and R5. This -22 volts will be applied directly through diode D2 to capacitor C1 and will change the voltage on rthis capacitor from its MM voltage 'of about +8 to -22 volts for the SM condition. The change in voltage on capacitor C1 will take a few nulli-seconds to complete. However, when the voltage has changed only from +8 to +4, transistor T2 will conduct. The change of voltage of this amount takes less than one milli-second.

When transistor T2 goes conducting, ythe +5 volts on its emitter is applied directly through the emitter-collector path of the transistor and through diode D5 to the a conducting condition in transistor'TZ Willpreveut tran-V sistor T3 from conducting.

'Considering the circuit-to the baise of transistor TV1, 4

' when the voltage of the receive hub was: +60, the voltage A'on the base of T1 was +22, and accordingly transistor T1 wasnon-conducting. When the voltage on the receive-hub goes to -30 for the SMor the MS condition, the voltage at the 'base .of transistor T1 goes to:.+l7 which still leaves transistorV T1 non-conducting.' There.- fore, during the SM condition lbeing described, transistorV T1 will remain non-conducting throughout and need not be considered in the holding action .on transistor T3 lunder discussion. Transistor T1 conducts only under `the SS condition.

When the receive relay returns to the marking condition it is necessary that the holding etlect of transistor T2 on transistor T3 remain for nearly the length of a unit pulse. This is ,to provide for the case where regenerative repeater is used betweenthe receive and send hubs, in which case the space on the output of the regenerativeV repeater will be lagging sometimes nearly a pulse length behind ,the space on the input when the receive leg signals have a large marking bias. It the hold on transistor T3 removed too soon, the last part of this space pulse will -be transmitted to the send line.

The `delay in the removal of the hold on the base of transistor T3 is obtained from the circuitry involving capacitor C71. During the SM condition the` voltage on the capacitor was about Y--22 volts and transistor T2 was conducting. When the receive relay goes to marking,

the positive +130 voltsV that appears at theriunction of R4 and R5 is blocked by diode D2 and must be` applied to the capacitor through R13 which has a high value. Transistor T2 Will therefore remain conducting until the voltage on C1 changesfrom .22 to about +5. The values of C1 and of R4 and R5 are selected so that this delay .is approximately one pulse length at sixty speed transmission or 22 nulli-seconds. It is, therefore, ample for H60 w,p.m., and also fior higher speeds which recuire less delay.

Thus, the complete holding action'is that when the lreceive relay goes spacing, the voltage on C1 ,changes quickly from a value of about +8 to the +4 value necessary to make transistor T2 conduct, and then continues on to a value of -22 volts for the steady state spacing condition. Then when the receive relay returns to marking, the voltage` on the capacitor slowly changes VLfrom -22 volts back to +8, holding transistor T2 con-Y ducting long enough to allow a space pulse being transmitted on the send ,leg by a regenerative repeater to vcorn- `pletebefore vtransistor T2 is made non-condueting and the hold onthe base of transistor T3 is removed.

,'If, while a space is being received on the receive relay and While Clis charged to -22 volts and transistor T2 is conducting tohold transistor T3 non-conducting, an-

other repeater associated with the receive hub sends a space to the hub (Condition SS)` the voltage on the hub will change from -'30 to -60 volts. This is the so-called 'double-space condition of the hub. Y

Y When the receive hub voltage becomes 60, the voltage applied to the base of transistor Ti becomes -5 and transistor T1 will conduct. During the conducting condition, of course, the voltage measured at the base of transistor'Tl will be the `same as the emitter voltage 4 which is +8 volts.Y

When transistor T1` conducts, it discharges C1 in less than a milli-second and causes the voltage on C1 to become +8. With the voltage on C1 equal to +8, tran- Y sistor T2 willV go non-conducting and remove the holding voltage from the 'base of transistor T3. Transistor T3 will thereforego conducting and operate the send relay -to spacing to ysend a space onvthe send line .of this repeater. This is called a double-space by-pass action, since of C1 and the change of transistor T2 from conducting to noni-conducting occurs in less Vthan one rnilli-second, thereis practically no delay in the vtransmission of the double space through the unit.

The presence of R17 being connected to the send hub ,is important as it performs two distinct functions. One is that 'it presents an artificial load to the send hub during Vthe marking condition. Its value is selected so that this load matches the load presented to the send hub during the spacing condition by the circuit to the base of transistor T3. The two loads are not equal in micro-amperes but are of such value that the voltage drop on the send hub is the same for both the mark and space condition. Thus, the addition of a considerable number of legs to the send hub will not cause bias since, with the mar-k and space loads on the send hub balanced for each coupling unit, it is comparable to a polar circuit in which decreasing the resistance of the circuit, and correspondingly increasing the current ow in the circuit does not cause bias because the increase is balanced for the mark and space conditions. y

Another function of Ri7 is Vto create more baseemitter current in transistor T3' during a time when the coupling units might be separated from the send hub. This will cause transistor T3 to conduct and send a denite space signal to the send line during such a condition, thereby giving a warning to the distant oiice that it is cut off the hub. If the send leg did not go open denitely under this condition, the distant end might remain in a closed condition and cut oft' lfrom the hub .for a considerable time before becoming aware it was no longer on the circuit. Without the added current from R17,

VVthe amount of base-emitter current in transistor T3 might be insuiiicient to drive the transistor completely conducting. The value of R17 is preferably in excess of 5 megohms with the voltages indicated in the drawing.

Diode D3 is connected around R9 so that when the voltage on capacitor C1 is positive this voltage will he applied to the base of transistor 'T2 through a low resistance instead of through the resistance of R9 which is high. This improves the perfor-mance of the transistor considerably at high temperatures since the leakage current that iows from collector to base in the transistor during high temperature conditions can not, in its tiow through diodes D3 and D6 and resistors R11 and R10, cause' sufficient voltage drop to change the voltage `at the base of transistor T'Zrfrom a positive to a negative value. Without the diode around R9, the leakage current would create such a voltage drop through this resistor lthat the voltage at the base of transistor T2 would become negative at `fairly low temperatures. When the voltage at the base o-f transistor T2 becomes negative with respect to the emitter, the transistor will conduct. This would cause a holding action on the base of transistor T3 even at times when Vtransistor T2 is intended Ato be non-conducting.' Signals would therefore be blocked on the send leg during times when they were supposed to be unblocked.

' Inhalt duplex` operation, assuming no regenerative rei peater, and a'low capacity hub, the conduction of transistor T2 when the receive relay goes spacing must occur before the voltage on the receive and send hubs in com- Vbination changes from +60 to +15, which isthe point duct very quickly. In the case of a very low capacity hub (only one or two legs connected), the voltage on the hub changes to the spacing value quickly enough to p make a slight change in the mark current through the send relay before the hold through transistor T2 is applied. This change of current is so slight that the armature of the relay does not operate at all and no harm is caused by the slight current kick that occurs. Under the condition of more legs on a hub, the change of voltage on the hub from mark to space will be slower and no current kick on the send relay winding current will be observed. When a regenerative repeater is used, the appearance of the space voltage on the send hub, of course, is delayed usually many milli-seconds and no kick at all will be observed in the send relay winding current.

In the case of full duplex operation, where the voltage on the receive hub changes from volts for mark to -60 volts for space, it is necessary that before the voltage on C1 can change sufficient to cause transistor T2 to conduct and place a hold on transistor T3, that transistor T1 be driven conducting to clamp C1 collector at the voltage of +8 which will hold transistor T2' nonconducting. This quick action of transistor T1 on full duplex operation is obtained through resistors R6, R7 and R8 and capacitor C2. It should be observed that the voltage at the junction of R7 and R8' is about -22 volts when the receive hub is at any value more positive than this, due to the blocking action of diode D7. When a space does occur on the receive hub, and the voltage changes from -10 towards -60, it will change only from -10 to -22 before the effect of the voltage change is transmitted through C2 to the base of transistor T1. Therefore, for only a l2 volt change in the voltage on the receive hub, transistor T1 will become conducting and clamp capacitor C1 at +8 volts. This action will occur before the voltage change on capacitor C1 due to the circuit through Rd has had time to bring the voltage on capacitor C1 to the value required to make transistor T2 conduct. Therefore, on full duplex operation where signals on the send side of the circuit must not be interfered with by signals on the receive side, any space pulse on the receive side will make transistor T1 conduct before transistor T2 can conduct and therefore transistor T2 can cause no hits to transmission on the send side. ln the case of added capacity to the receive hub, the change of the voltage from l0 to -60 on a space will occur more slowly. If it occurred slowly enough, transistor T1 would be slow in becoming conducting and transistor T2 would conduct momentarily before transistor T1 became conducting, and, during a time when a space was being transmitted on the send side, a mark-to-space transition on the receive side would cause a marking hit on the send side. The circuit of the present invention will operate at full duplex with a capacity of over .5 MF on the receive hub, which is considerably more capacity than would exist in practice on full duplex operation.

On half duplex operation, the network to the base of Tl causes no load on the receive hub for the MM condition, and only causes a load when the voltage on the hub reaches -22 volts or more. This voltage is considerably beyond the changeover voltage of at which the send hub is to go from mark to space. Therefore,`

the operation of the send relay will have occurred before the network produces any load on the hub and ktherefore the network will cause no bias to signals even when l5 to coupling units are connected to the same hub.

Resistors Ri and R2 comprise the circuitry for the hit locator of a No. 2 service board. These resistors are the same as are used in the prior l44A1 unit and the theory of operation is the same.

The invention may be embodied in other specific forms Without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and described to be secured by United States Letters Patent is:

`1. A hub telegraph repeater unit of the type adapted to be connected to a receiving hub and a sending hub, said repeater unit comprising: a receiving leg having a receiving relay connected to said receiving hub through an impedance, a sending leg having a sending relay connected to said sending hub through an impedance and a tirst transistor normally non-conducting to causerthe sending relay to be in a marking condition; a iirst control stage having a second transistor normally non-conducting when the receiving leg is at rest; circuit means for connecting said second transistor to said first transistor for preventing said iirst transistor from conducting even though a space signal condition is present on said sending hub; means including a resistance, diode and capacitor connected to said receiving leg between said receiving relay and Vsaid impedance for selectively charging said capacitor when said receiving leg has a space signal thereon; means for connecting one terminal of said capacitor to said second transistor to cause said second transistor to control said rst transistor and prevent the sending leg from transmitting a space signal; and a second control stage comprising a third transistor; circuit means for connecting said third transistor to said receivingrhub and to said one terminal of said capacitor for preventing said capacitor from becoming charged when a space signal condition is simultaneously supplied to said receiving hub from a plurality of receiving legs.

2. In a hub telegraph repeater unit adapted to be connected to a receiving hub and a sending hub, said unit having a control circuit interconnecting receiving and sending legs for a single circuit for locking and unlocking said sending leg in response to signaling conditions impressed on said receiving leg comprising a first transistor having base, collector and emitter elements, a first circuit means connecting the base element of said first transistor to said sending hub, means for connecting the emitting element of said first transistor to send relay windings in said sending leg and through a rst inipedance to a source of positive potential whereby the current conduction of said first transistor controls the operation of the sending leg, means connecting said collector element to a first source of relatively small negative voltage through a diode and to a second source of larger negative voltage through a second impedance, and a third impedance connected from a common connection between said small negative voltage source and said diode to ground, said diode being so poled as to protect the transistor from excessive collector voltages.

3. The repeater unit as defined in claim 2 further having a fourth impedance connected between said emitter element and ground to prevent excessive voltage on the emitter element when the send relayv windings are removed from said repeater.

4. The repeater unit as defined in claim 3 further having in said rst circuit means an impedance having a resistance of at least 5 megohoms connected to a negative voltage source of volts to match the load presented to the send hub and to create added base-emitter current in said transistor so that if said transistor should become disconnected from said send hub, a space condition will be sent to the distant oflice connected to said send leg thereby warning it has been cut-off from said sending hub. Y

5. In a hub telegraph repeater unit adapted to be connected to a receiving hub and a sending hub, said unit having a control circuit interconnecting receiving and sending legs for a single circuit for locking and unlocking said sending legs in response to signaling conditions impressed on said receiving leg comprising: a rst transiStOr; `a first circuit means including a large impedance connecting a .control element `of said frst Y'transistor to saidrsending hub; means for connecting another element of said tirst transistor to said sending leg whereby the current Vconduction of said irst transistor controls the operation of the sending leg; a second transistor having emitter, collector' and base elements with the coliector element connected to control current conduction through said rst transistor through a circuit having low impedance whereby the current conduction through said lsecond transistor is eiective to override the signal on the send hub in the ycourse of controlling current conduction in said first transistor;and a second circuit means including a rectifier, resistance and capacitorconnected to said second transistor for controlling the current conduction through said second transistorgthe charge on said condenserchanging relatively quickly when a space signal is present on said receivingieg to effect a change inthe conduction condition of said second transistor, and

'changing much more slowly when a'rnark signal follows the space signal to provide a delay equal to approximately one pulse length of the telegraph code beingV transmitted before eiecting a further change in the current conduction condition of said second transistor.

6. The repeater unit as deined in claim wherein one terminal von said capacitor is connected Vto the base element of said second transistor through a paralrel circuit comprising a resistance and a diode, the diode being ,poled sothat leakage current that flows from the collector to base elements at high temperatures causes insuiiicient voltage drop across said resistance to change the conduction condition -of said second transistor.

' v7. The repeater nnit as defined in claim 6 wherein said second `circuit means is connected to the receiving leg at a point between thereeeivev relay and the receive hub. A

8. The repeater unit asdeiined in clairn 5 further having a third transistor having collector, base and emitter elements with its collector element connected to one terminal of said capacitor, its emitter element connected to a potential positive relative to they potential of the emitter element of said second transistor, and its base element connected to said receive` hub whereby a double space on said receiveV hub causes said third transistor to conduct and thereby change the charge on said capacitor to prevent said second transistor from being in a conductive condition. Y

9.- The repeater unit as defined in claim 8 wherein the connection between thebase element on said third transistor and said receive hub comprises a voltage divider and diode to increase the speed of response of said transistors to enable full duplex operation.

- y References Cited in the tile of this patent UNITED STATES PATENTS 2,558,197Y Rea June 26, 1951 2,607,852 Rea Aug. 19, 1952 2,612,560 Rea Sept. 30, 1952 v2,636,942 Davey Apr. 28, 1953 OTHER REFERENCES Electronic and Radio Engineering, by F. E. Terman;

McGraw-Hill Book Co., fourth edition, copyright 1955, pages 632, 633, 777-781, 795.y 

